I suppose something in the function is rigid that the shape of the subset array has to be the same as the "Latitude" and "longitude". It's all a problem of knowing the dimensions - if the function can recognize that the 3rd (or beyond) dimension, "nWavel" in this case, is not shared with those of the "Latitude" and "Longitude", but rather with a different variable which may or may not need subset (nWavel in this case, specified in the URL for subset), the function may execute correctly.